Process for coating flexible sheet with amylose



July 4, 1967 R. w. BEST ETAL 3,329,523

PROCESS FOR COATING FLEXIBLE SHEET WITH AMYLOSE Filed June 29, 1964United States Patent O 3,329,523 PROCESS FOR COATING FLEXIBLE SHEET WITHAMYLOSE Roland W. Best and Robert M. Powers, Decatur, Ill., as-

signors to A. E. Staley Manufacturing Company, Decatur, 11]., acorporation of Delaware Filed June 29, 1964, Ser. No. 378,924 19 Claims.(Cl. 117-64) This is a continuation-in-part of application Ser. No.296,660, filed July 22, 1963, and now abandoned.

This invention relates to a continuous process of forming an amylosicfilm or coating on paper.

For many years there has been a demand for low-cost grease-resistantcoatings for paper. When amylosic material first became commerciallyavailable, it was thought that amylosic material might satisfy the needfor a lowcost grease-resistant coating for paper. Insofar as we havebeen able to ascertain, this has only been conjecture. Until now, no onehas disclosed any method for forming smooth, grease-resistant amylosiccoatings on paper webs.

A variety of processes have been used for the continuous production ofamylosic films. These processes include the extrusion of amylosicsolutions into a coagulating bath, which precipitates the film; theextrusion of superficially 'dry amylosic material; casting amylosicsolutions on a moving belt or roll under conditions where solvent isevaporated, forming an amylosic film; etc. However, all of theseprocesses are designed for the preparation of self-supporting amylosicfilms and are not suitable for the preparation of'smooth,grease-resistant amylosic coated paper webs. Further, the tendency ofamylosic material to gel rapidly, which is often advantageous in castingself-supporting amylosic films, is a drawback in the preparation ofgrease-resistant paper.

While it might appear that grease-resistant coatings could be applied topaper by passing the paper Web through an amylosic solution, such is notthe case. When a paper web is passed through an amylosic solution, theweb must be passed through a nip in order to remove excess treatingmaterial and to form a smooth surface. In this treatment the amylosicmaterial is forced into the interior of the paper. When such paper is incontact with a greasy substance, the cellulosic fibers seem to act as awick, for the grease passes through the paper. It is almost impossibleto form a smooth amylosic coating with a spray applicator because of thetendency of aqueous solutions of amylosic material to gel prematurelybefore the active material can uniformly cover the paper.

Our own work has shown that it is virtually impossible to form anaesthetically acceptable smooth grease-resistant coating on a singlesheet of paper (for example, 45 pound paper stock) using any of thecommonly used laboratory hand coaters, such as a Bird applicator,Gardner applicator, doctor blade, Nordson Airless spray applicator, wirewrapped rod, etc. These failures are due to a combination of the porous,uneven character of paper and the tendency of aqueous solution ofunderivatized amylosic material to gel rapidly as the concentration ofamylosic material increases and/or as the temperature of the aqueoussolution decreases. The rapid gelling properties of amylose make italmost impossible to smooth a single sheet of paper prior to thegelation of the amylosic layer.

The object of this invention is to provide a continuous method offorming grease-resistant amylosic-coated paper webs.

We have now found that grease-resistant amylosic coated paper webs canbe produced continuously and efliciently by applying an aqueous solutionof amylosic material to the paper web with a roll applicator, followedICC almost immediately by a smoothing operation before the amylosiccoating can gel. Any excess coating material can be removed with an airblast from an air knife or by passing the coated side of the paper webover a rotating r-od. In this way a smooth grease-resistant sheet isobtained. The combination of roll applicator and air-knife smootherisknown as an air-knife coater, while the combinat-ion of a rollapplicator and rotating-rod smoother is known as a Champion knifecoater. Of these two, the air-knife is preferred since it is possible toapply a much heavier amylosic coating in a single pass.

The drawing illustrates a typical roll applicator of the air-knifecoater variety. In a typical coating operation utilizing the principlesof this invention, an aqueous slurry of from about 1% by weight to 15%by weight amylosic material is prepared. The amylosic material is thendissolved by heating the aqueous slurry under pressure in a continuousheat exchanger to about 120 C. to 160 C. or higher in order to dissolvethe amylosic material. The dissolved amylosic material is continuouslydischarged into a ooacting pan 1 which is maintained above the gelationtemperature of the amylosic solution (typically 60- C.). The rollapplicator 3, which can be heated if desired, almost immediately reachesthe temperature of the amylosic solution in the coating pan 1 as theroll applicator 3 revolves. The roll applicator 3 transfers the hotamylosic solution to the paper web 5. The paper web 5 which is typicallymoving at about 50 to 2500 feet per minute passes over the top of theapplicator roll 3 and around the breast roll 7. An air knife 9 removesexcess treating material and smoothes the surface of the paper bypropelling a blast of air against the paper passing around the breastroll 7. Because of the speed at which the web is moving, the smoothingoperation takes place immediately after the coating has been applied,before the amylosic material can gel. The excess treating material iscaught in the catch pan 11 which can be heated to keep the amylosicmaterial in fluid form. The amylosic material caught in the catch pancan then be recycled to the coating pan. The coated paper is then driedand wound upon a suitable roll. If desired, prior to or after the dryingstep the amylosic coated paper web can be coated with one or moreadditional coatings of amylosic material and/or other treatingmaterials.

For the purpose of this invention, the term amylosic material refers tothe amylose resulting from the separation of the amylose and amylopectincomponents of starch, or the whole starch which is composed of at least50% amylose. Commercially available sources of amylose include Nepolamylose (the amylose fraction of corn starch), Superlose (the amylosefraction of potato starch), Amylomaize or Amylon (high-amylosic materialcorn starch containing approximately 54% amylose), Amylon VII(high-amylose corn starch containing up to 70% amylose), etc. Theamylosic coatings based on high-amylose corn starch can be simulated bymixing corresponding concentrations of separated amylose with separatedamylopectin. Preferably, the amylopectin content of the amylosicmaterial is less than 20% by Weight since the higher the concentrationof amylose the better the flexibility and strength of the coating.Various derivatives of amylosic material (amylose acetate, hydroxyethylamylose, hydroxypropyl amylose, etc.) such as those described in US.Patent 3,038,895 can also be employed.

As indicated above, the coating composition is usually prepared by firstforming an aqueous slurry of from about 1% to 15 by weight amylose andthen dissolving the amylosic material at about C. to 200 C. in acontinuous heat exchange unit, such as a Votator or any of the commontypes of starch cooker. In general, the higher the concentration ofamylosic material in the coating composition the heavier the coating ofamylosic material that can be applied to the paper in a single pass andcorrespondingly the more grease-resistant the paper. However, the higherthe concentration of amylosic material the higher the viscosity of thecoating composition and the greater the tendency of the amylosicmaterial to gel prematurely in the coating pan or before the smoothingstep. Accordingly, it is preferred to employ aqueous coatingcompositions containing from about 6 to 12% by weight dissolved amylosicmaterial.

In order to prevent premature gel formation and high viscosity, theamylosic solution in the coating pan is kept hot, preferably at atemperature of about 60 C. to 100 C. However, the temperatures as low as25C. can be employed with dilute aqueous solutions of the order of about1% by weight amylosic material. In general, the temperature and amyloseconcentration should be selected in a manner to provide a coatingcomposition having a maximum viscosity of about 400 cps. as measured ona Brookfield viscometer. However, in some cases, viscosities as high as1,000 cps. can be employed.

The above processing conditions are most suitable when the nowcommercially available forms of underivatized amylose and granularhigh-amylose corn starch are employed. However, other forms of amylosicmaterial, which dissolve in cold water or boiling water (100 C.), suchas many of the amylosic derivatives described in U.S. Patent 3,038,895and unretrograded amylosic material described in U.S. Patent 3,086,890,can be dissolved at lower temperatures. Likewise, the coatingcomposition itself can be maintained at a lower temperature if anamylosic derivative of reduced tendency to gel is employed. In additionto various amylosic derivatives, which dissolve in water at less than100 C., amylosic derivatives of the type described in commonly assignedapplication Ser. Nos. 65,295, now U. S. Patent 3,127,392, and 73,190,now U.S. Patent 3,208,998, which dissolve in water at temperatures above100 C. but form stable aqueous solutions can be used. Further, someamylosic derivatives which are less viscous than underivatized amylosicmaterial, can be employed at higher concentrations up to about 20% byweight. However, for best results, the temperature and concentration ofamylosic derivatives should be selected in a manner to provide a coatingcomposition having a maximum Brookfield viscosity of about 400 cps.

The amylosic coating composition can, of course, have additionalingredients. For example, plasticizers, such as glycerol, sorbitol,choline chloride, etc., are useful for increasing the flexibility andelongation of the amylosic coating. Polyvinyl alcohol and/or1,2,6-hexanetriol are particularly effica-cious additives.

As indicated above, the amylosic coating can be applied in a single passor in several passes. However, for forming effective grease-resistantpaper, We have found that the amylosic coating (amylosic material andother additives, such as plasticizers) must weigh at least one pound per1000 square feet of paper and preferably at least two pounds per 1000square feet of paper. At lower coating weights the paper can be used inoffset printing, where it is noly necessary to slow down the penetrationof the hydrophobic printing ink.

The following examples are merely illustrative and should not beconstrued as limiting the scope of our invention.

Example I An aqueous solution of defatted amylose was prepared at 155 C.by passing a total solids aqueous slurry (8.5 parts by weight amyloseand 1.5 parts by weight amylopectin) through a starch cooker of the typedescribed in application Ser. No. 790,487 filed Feb. 2, 1959, now U.S.Patent 3,101,284. The solution was continuously supplied to a preheatedcoating pan (70 C.) of an airknife coater. (The air-knife coater was onestation on a 40 foot long pilot plant coater.) The aqueous solution ofamylose was continuously applied to a surface of a roll, which waspartially immersed in the coating pan. The surface of the roll was notwater absorptive. The amylose, while in an ungelled state, wastransferred from the surface of the roll to a paper web (a roll of 45pound paper), which was moving at 250 feet per minute. Immediatelythereafter, before the overlying amylose coating composition gelled, thecoating was smoothed by passing the paper web between a roll surface andan air blast from a jet. The coated side of the paper was exposed to theair blast. The coated paper was dried and then run through the air-knifecoater a second time. The paper, which was dried a second time, had anamylose coating of about 1.1 pounds per 1,000 square feet of paper.

A 4 inch by 4 inch square of paper passed the standard grease-proofingtest of the Technical Association of the Pulp and Paper Industry. Thebackside of the coated paper showed no passage of dye when 1.1 ml.turpentine containing an oil soluble red dye was dropped on a five grammound of sand, which was placed on the coated side of the paper.

Example 11 Example I was repeated except that a roll of bleached kraftpaper was used and the first amylose coating solution was prepared froma 12% by weight aqueous slurry of amylose. Paper having one layer ofamylose, about 0.6 pound per 1,000 square feet of paper, failed the testdescribed in Example I. Paper coated with a second layer of amylose,with a coating weight of about 2.0 pounds per 1,000 square feet ofpaper, passed the test described in Example I.

Example III Example I was repeated except that a roll of bleached kraftpaper was used and three coats of amylose was applied to most of theroll. The paper which had been coated with two layers of amylose had acoating weight of about 2.3 pounds while the paper which had been coatedwith three layers of amylose had a coating weight of about 3.4 poundsper 1,000 square feet of paper. Both coated papers passed the testdescribed in Example I.

Example IV This example illustrates coating the polyethylene side ofcommercially available corona discharge treated polyethylene coatednatural kraft paper, the polyethylene layer being approximately 0.50 milthick. An aqueous solution of amylose was prepared by heating to 155 C.a 11% solids aqueous slurry of 7.2 parts by weight corn amylose, 0.8part by weight corn amylopectin and 3 parts by weight polyvinyl alcoholhaving about 2 acetyl groups per each monomeric units. The amylosecomposition was applied to the polyethylene side of the flexible sheetin the manner described in Example I, dried and a second coat applied inthe same manner. The coated sheet passed the grease-proofing testdescribed in Example I.

Example V Example I was repeated with essentially the same resultsexcept that the amylose composition was applied to the coated side of apaper web which had been sized with a composition comprising clay and14% by weight alkaline hypochlorite-oxidized starch based on the weightof the clay.

While the preceding examples illustrate the application of amylosicmaterial to paper (coated and uncoated) with an air-knife coater thesame coating technique can be used to coat any flexible sheet withamylosic material. For the purposes of this invention the term flexiblesheet includes films or coatings of polyethylene, polypropylene,polyethylene terephthalate, polyvinylidene chloride, polyvinyl chloride,polyvinyl fluoride, aluminum foil, etc.

The term paper is used in a generic sense to include paper of allvarieties, whether coated or uncoated, including paper board.

Since many embodiments of this invention may be made and since manychanges may be made in the embodiments described, the foregoing is to beinterpreted as illustrative only and our invention is defined by theclaims appended hereafter.

We claim:

1. The process of forming a smooth, grease-resistant coated flexiblesheet which comprises the steps of (1) providing an aqueous solutionconsisting essentially of an amylosic material containing at least 50%by weight amylose, wherein said amylosic material is present in aconcentration of from 1 to 20% by weight of said aqueous solution and isselected from the group consisting of the separated amylose fraction ofwhole starch, Whole starch containing at least 50% by weight amylose andmixtures thereof, (2) applying said aqueous solution of amylosicmaterial to a surface which is not water absorptive, (3) while saidamylosic material is in an ungelled state transferring the coatingcomposition from said surface to a flexible sheet, while said flexiblesheet is moving at a rate of about 50 to 2,500 feet per minute, (4)immediately smoothing said coating before the overlying amylosic coatingcomposition gels, and (5) drying said flexible sheet.

2. The process of claim 1 wherein said flexible sheet is a continuouspaper web.

3. The process of claim 2, wherein said aqueous solution of amylosicmaterial has a maximum Brookfield viscosity of 400 cps.

4. The process of claim 2, wherein said aqueous solution of amylosicmaterial is at a temperature of from about 60 C. to 100 C.

5. The process of claim 4, wherein said amylosic material is theseparated fraction of whole starch and comprises no more than 15% byweight of said aqueous solution.

6. The process of claim 5, wherein said amylosic material comprises fromabout 6% to 12% by weight of said aqueous solution.

7. The process of claim 4, wherein the amylopectin content of theamylosic material is less than 20% by weight and said amylosic materialcomprises no more than 15% by weight of said aqueous solution.

8. The process of claim 2, wherein excess amylosic treating material isremoved from the coated paper in the smoothing operation and recovered.

9. The process of claim 8, wherein the excess amylosic material isrecycled.

10. The process of forming a smooth, grease-resistant coated flexiblesheet which comprises the steps of (1) providing an aqueous solutionconsisting essentially of an amylosic material containing at least 50%by weight amylose, wherein said amylosic material is present in aconcentration of from 1 to 20% by weight of said aqueous solution and isselected from the group consisting of the separated amylose fraction ofwhole starch, whole starch containing at least 50% by weight amylose andmixtures thereof, (2) applying said aqueous solution of amylosicmaterial to a surface which is not water absorptive, (3) while saidamylosic material is in an ungelled state transferring the coatingcomposition from said surface to a flexible sheet, while said flexiblesheet is moving at a rate of about 50 to 2,500 feet per minute, (4)immediately smoothing said coating before the overlying amylosic coatingcomposition gels by passing said flexible sheet between a surface and ablast of air with the coated side of the flexible sheet being exposed tothe blast of air, and (S) drying said flexible sheet.

11. The process of claim 10 wherein said flexible sheet is a continuouspaper web.

12. The process of claim 11, wherein said aqueous solution of amylosicmaterial has a maximum Brookfield viscosity of 400 cps.

13. The process of claim 11, wherein said aqueous solution of amylosicmaterial is at a temperature of from about 60 C. to C.

14. The process of claim 13, wherein said amylosic material is theseparated fraction of whole starch and comprises no more than 15% byweight of said aqueous solution.

15. The process of claim 14, wherein said amylosic material comprisesfrom about 6% to 12% by weight of said aqueous solution.

16. The process of claim 13, wherein the amylopectin content of theamylosic material is less than 20% by weight and said amylosic materialcomprises no more than 15% by weight of said aqueous solution.

17. The process of claim 12, wherein excess amylosic treating materialis removed from the coated paper by the air blast.

18. The process of claim 17, wherein the excess amylosic material isrecycled.

19. The process of claim 11, wherein said amylosic coating compositioncontains a plasticizing concentration of a polyhydric alcohol.

References Cited UNITED STATES PATENTS 2,325,798 8/1943 Porter 117156 X2,798,990 7/1957 Davis 117165 X 2,822,581 2/ 1958 Muetgeert et al.106-210 X 2,949,382 8/1960 Dickerman et a1. 117156 X 3,076,720 2/1963Rice et al 11786 X FOREIGN PATENTS 6,410,751 9/ 1964 Netherlands.

OTHER REFERENCES Egan, F. W., Some Fundamentals of Coating Methods. ThePaper Industry and Paper World, pp. 1142-4145, December 1944, copy in117111.

Kaplan, Paul, Potential Industrial Use of Amylose. Cereal Science Today3(8) pp. 206-209, October 1958, TH c 34.

WILLIAM D. MARTIN, Primary Examiner.

MURRAY KATZ, Examiner.

H. W. MYLIUS, M. LUSIGNAN, Assistant Examiners.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,329,523 July 4, 1967 Roland W. Best et a1.

d that error appears in the above numbered pat- It is hereby certifietters Patent should read as ent requiring correction and that the saidLe corrected below.

Column 2, line 21, for "coacting" read coating line 49, for "amylose",second occurrence, read amylosic material lines 52 and 53, for"(high-amylosic material corn" read (high-amylose corn line 68, for"amylose" read amylosic material column 3, line 17, for "amylose" readamylosic Signed and sealed this 18th day of June 1968.

(SEAL) Attest:

EDWARD J. BRENNER Commissioner of Patents Edward M. Fletcher, Jr.

Attesting Officer

1. THE PROCESS OF FORMING A SMOOTH, GREASE-RESISTANT COATED FLEXIBLESHEET WHICH COMPRISES THE STEPS OF (1) PROVIDING AN AQUEOUS SOLUTIONCONSISTING ESSENTIALLY OF AN AMYLOSIC MATERIAL CONTAINING AT LEAST 50%BY WEIGHT AMYLOSE, WHEREIN SAID AMYLOSIC MATERIAL IS PRESENT IN ACONCENTRATION OF FROM 1 TO 20% BY WEIGHT OF SAID AQUEOUS SOLUTION AND ISSELECTED FROM THE GROUP CONSISTING OF THE SEPARATED AMYLOSE FRACTION OFWHOLE STARCH, WHOLE STARCH CONTAINING AT LEAST 50% BY WEIGHT AMYLOSE ANDMIXTURES THEREOF, (2) APPLYING SAID AQUEOUS SOLUTION OF AMYLOSICMATERIAL TO A SURFACE WHICH IS NOT WATER ABSORPTIVE, (3) WHILE SAIDAMYLOSIC MATERIAL IS IN AN UNGELLED STATE TRANSFERRING THE COATINGCOMPOSITION FROM SAID SURFACE TO A FLEXIBLE SHEET, WHILE SAID FLEXIBLESHEET IS MOVING AT A RATE OF ABOUT 50 TO 2,500 FEET PER MINUTE, (4)IMMEDIATELY SMOOTHING SAID COATING BEFORE THE OVERLYING AMYLOSIC COATINGCOMPOSITION GELS, AND (5) DRYING SAID FLEXIBLE SHEET.